1. Technical Field
The present disclosure relates to an oxide thin film transistor, and more particularly, to a method of manufacturing an oxide thin film transistor, in which an oxide thin film transistor having improved performance is manufactured through surface treatment of an active layer made of an oxide semiconductor.
2. Discussion of the Related Art
A liquid crystal display device of flat panel display devices is a device that displays an image by using optical anisotropy of a liquid crystal, and is used for a notebook computer, a desktop monitor, etc.
The liquid crystal display device includes a color filter substrate, a thin film transistor substrate, and a liquid crystal layer interposed between the color filter substrate and the thin film transistor substrate.
An active matrix mode which is a driving mode used for the liquid crystal display device uses an amorphous silicon thin film transistor as a switching element.
The amorphous silicon thin film transistor used for the aforementioned liquid crystal display device may be manufactured by a low temperature process but has very small mobility. On the other hand, although a polycrystalline silicon thin film transistor has high mobility, problems occur in that it is difficult to obtain a large area due to difficulty in obtaining uniform properties and a high temperature process is required.
In this respect, an oxide thin film transistor in which an active layer is formed of an oxide semiconductor has been developed.
FIG. 1 is a cross-sectional view illustrating a structure of a general oxide thin film transistor according to a related art.
As shown in FIG. 1, the general oxide thin film transistor includes a gate electrode 21 formed on a substrate 10, a gate insulating film 22 formed on the gate electrode 21, an active layer 30 formed of an oxide semiconductor on the gate insulating film 22, source and drain electrodes 41 and 42 electrically connected with a predetermined region of the active layer 30, a passivation film 50 formed on the source and drain electrodes 41 and 42, and a pixel electrode 70 electrically connected with the drain electrode 42.
Generally, the active layer 30 formed of an oxide semiconductor is formed in such a manner that an oxide semiconductor layer is deposited on the gate insulating film 22 by sputtering and then selectively patterned using a photolithography process.
According to the related art, as oxygen density in a reaction gas is controlled during the sputtering process for forming the oxide semiconductor layer, carrier density of the active layer is controlled, whereby switching element properties of the oxide semiconductor may be obtained.
At this time, properties as a switching element of the active layer made of an oxide semiconductor and uniformity of element properties in a glass and between glasses or lots due to oxygen density change are determined by the oxygen density control.
However, since improving conditions of the sputtering process for deposition of the oxide semiconductor is limited, a problem occurs in that it is difficult to improve performance and uniformity of the active layer.